1. Field of the Invention
The present invention relates to a focused ion beam system and a composite charged particle beam device for preparing a sample for a transmission electron microscope.
2. Background Information
Focused ion beam systems are widely used to prepare a sample for a transmission electron microscope (TEM). Particularly, in fields of process monitoring and failure analysis for semiconductor devices, the preparation of a sample by a focused ion beam is an essential technique because positioning accuracy of a sample piece is very high.
The preparation of a TEM sample by a focused ion beam is performed such that a thin observing piece is prepared by positioning a site to be observed in a sample by an ion microscope image of a focused ion beam system and removing both sides of an observing cross section by ion beam etching. The prepared thin piece is moved to a sample table for TEM observation to be subjected to the TEM observation.
The cases where a TEM sample is required to have a thickness of 100 nanometers or less increase due to the miniaturization of semiconductor devices. Such an extremely thin sample has a high risk of being damaged while being moved to a sample table for TEM observation. Therefore, in many cases, the thin sample is prepared thick to a certain extent to be transferred to the sample table for TEM observation and is finally thinned on the sample table for TEM observation. A typical size of the thin TEM sample piece is about 10 micrometer squares and a thickness thereof is about several micrometers. There is an example in which a manipulator in which a needle having a very sharp tip end is mounted on an actuator capable of performing a precision operation is used to handle such a tiny sample. The needle is brought close to the sample to be fixed thereto by ion beam deposition, and the sample is brought close to the TEM sample table by the operation of the actuator and a sample stage. Then, the ion beam deposition is performed again to fix the sample to the sample table. Normally, these operations are performed in a visual field of a focused ion beam system, and thus freedom in operation of the manipulator is small. Accordingly, the extracted sample is fixed to the sample table in the same posture as that at the time when the sample is extracted. In many cases, a wiring layer on the upper side and a substrate on the lower side in a semiconductor sample are fixed to a sample table.
In this state, final thinning is performed. However, a finished state of the thinning on the lower part of the sample may be influenced by the structure of the upper part thereof since efficiencies of etching by an ion beam are different for sites such as a wiring part, an interlayer insulation film and the substrate. Such an influence of the structure of the upper part is acknowledged as a problem in observation of the vicinity of a gate oxide film of a MOS transistor or in observation of a bottom of a via.
In order to solve such a problem, Patent Document 1 discloses a method of isolating a sample matrix from the back side to be turned upside down and a method of using a manipulator having a rotation axis and a tilt mechanism. In the method of isolating a sample matrix from the back side to be turned upside down, sites to be subjected to the TEM observation in a majority of samples are disposed at a depth of about 10 um from the front side, but at a depth of several hundred micrometers or more from the back side. Thus, it is required to perform special preprocessing such as preliminary polishing of the back side to extract samples from the back side. Further, it is very difficult to detect a polishing endpoint and there is a big problem in practicality. In the method of using a manipulator having a rotation axis and a tilt mechanism, a tilt of about several ten degrees is required in response to a manipulator attachment angle. It is considered that a translation mechanism is required which has a stroke of about several ten millimeters as well as a tilt in order to place a target sample in a visual field of a focused ion beam system with a tilt of several ten degrees. In addition, in a composite system of a focused ion beam system and an electron scanning microscope, which is in widespread use in recent years, a space near a sample is greatly restricted, and thus it is anticipated that it is very difficult to mount these mechanisms.
The importance of a method of fixing a sample piece of which a posture is rotated to a TEM sample table and finally thinning the sample piece is widely recognized, however, a device for efficiently performing the process of extracting a thin TEM sample piece, shifting a posture and fixing the thin TEM sample piece to a sample table is not yet provided.
[Patent Document] JP-A-2007-108105
In consideration of the technical trends described above, a task of the invention is to provide a sample preparing device in which a posture of a sample piece is easily rotated by 90 degrees, 180 degrees or an arbitrary number of degrees to fix the sample piece to a sample table.